1. Field of the Invention
The present invention relates to coating compositions containing fluorescent colorants, more particularly, to coatings containing fluorescent colorants that appear to change color with varying levels of light intensity.
2. Prior Art
Colored coating compositions typically include colorant particles dispersed in a resinous binder. The coating composition may further include reflective pigments, such as aluminum flake or metal oxide coated mica or other color effect pigment compositions or substrate-hiding materials, such as titanium dioxide. Conventional automotive solid-colored coatings include a resin and colored pigments which determine the desired coloration of the coating. Typically, solid color pigments are of a size such that they will scatter incident light effectively. The scattering will be in all directions.
Conventionally, in a pigmented coating composition, light that is scattered back out of the coating is described as being diffusely reflected while light that is scattered forward through the coating composition and is described as diffuse transmission. This scattering, in particular diffuse reflectance, is often desirable, providing opacity to the coating and hiding the surface of a coated article. Solid color pigments also typically absorb a portion of the incident light such that the light that is diffusely scattered and the remainder that is diffusely transmitted has a perceived color. These coating compositions may include a reflective pigment such as aluminum flake or metal oxide coated mica or other color effect pigment compositions. The portion of the incident light that is not absorbed or diffusely reflected by the colored pigment will interact with these color effect pigments. This portion of incident light may be specularly reflected by aluminum flake, or may interact with the coated mica or other effect pigment to produce a reflection whose perceived color is influenced by the structure of the pigment via an interference phenomenon. If this portion is specularly reflected by aluminum flake, there may be a perceived change in the color of the coating composition, typically described as flop. The perceived color will appear bright at viewing angles close to specular (on face), and appear to darken at viewing angles far from specular (on flop).
Such color effect pigments and coating compositions are desirable in the marketplace as styling tools in automotive coatings. However, angle-dependent color effect pigments are costly to prepare. The perception of color by the human eye is dependent on many factors, not the least of which is the environment surrounding a colored surface. One readily available environmental feature that affects the color of automotive coatings is the presence and intensity of sunlight. Some colors appear different in shade than when in direct sun. The advantages of producing color effects in coating compositions based on variable environmental light levels have not been fully exploited.
Accordingly, a need remains for producing cost-effective color effect coating compositions for use as alternative styling tools which use the surrounding light levels to control the perceived color of a coating composition.